This invention pertains generally to transport apparatus and more particularly to transport apparatus of the type in which an elongated strip of pliant material, such as magnetic recording tape or film, is wrapped to form supply and take-up rolls and a drive capstan peripherally engages the rolls to rotate the same and feed the strip from the supply roll to the take-up roll.
In such apparatus, the tape must be maintained in a tensioned condition between the supply and take-up rolls in order to maintain proper control of the tape. After the tape has been loaded onto the transport and first threaded from the supply roll to the take-up hub, it is usually slack or untensioned in the span between rolls, and for proper tape control, it is imperative that tensioning commence as soon as the tip of the tape or leader is captured between the capstan and the take-up hub.
Heretofore, there have been attempts to tension the tape during the threading operation by applying a drag brake to the supply roll. Such attempts have not been satisfactory, however, because the brake must be applied with sufficient force to produce a controlled slippage between the supply roll and capstan. At the same time, the brake must not be applied with so much force that the supply roll stops completely or turns erratically or the threading process may be undesirably prolonged or actually never completed. In practice, it is difficult to maintain the proper braking force.
In order to eliminate the need for critical braking force control, there have been attempts to delay the application of the brake until the tip of the tape or leader is actually captured between the supply roll and the capstan. This approach requires precise timing and therefore means such as a relatively expensive sensor or timer for detecting the capture of the tip.